A catalyst is used in various chemical reactions. Generally, the catalyst is recovered from a reaction mixture containing a reaction product and recycled to the reaction system in an industrial plant. The main purpose of the recovery and recycle of the catalyst is to reduce costs.
A telomerization reaction of perfluoroalkyl iodide with tetrafluoroethylene is one of the chemical reactions wherein recovery and recycle of a catalyst are carried out. The perfluoroalkyl iodide telomers obtained by the telomerization reaction are useful chemicals as a material for a surfactant or a water- and oil-repellant applied to fiber.
There is disclosed that copper powder is used as a catalyst for the telomerization reaction in “Copper-Induced Telomerization of Tetrafluoroethylene with Fluoroalkyl Iodides”, Chen et al., Journal of Fluorine Chemistry 36 (1987), pp. 483 to 489. The advantage of the telomerization reaction which employs copper powder is that the reaction proceeds at a relatively low temperature between 80 and 100° C., and that a shorter reaction time is required to accomplish a certain result compared with a telomerization reaction wherein an organic peroxide is used as a catalyst.
The copper catalyst which has been used in the telomerization reaction is recovered by, for example, drawing a reaction mixture from a reactor and carrying out a solid-liquid separation operation outside the reactor. The “reaction mixture” means a mixture which contains a catalyst in a solid phase and a reaction product in a liquid phase, and may further include an unreacted starting material. The recovered catalyst is mixed with the starting material and so on and recycled to the reactor for reuse. It is difficult to continuously carry out this catalyst recovery and recycle method since the method accompanies complicated operations.
The inventors of the present invention have studied the applicability of an apparatus which is disclosed in Japanese Laid-Open (Kokai) Publication No. 11-286457 (1999) to the telomerization reaction. That is, the inventors have studied the possibility of using an apparatus wherein a filter is immersed in the reaction fluid which includes the catalyst and the perfluoroalkyl iodide telomers obtained by the telomerization reaction. The filter is a porous filter such as a sintered metal filter. This apparatus enables the telomerization reaction and the catalyst recovery to be conducted simultaneously. Conducting a chemical reaction (for example, the telomerization reaction) “continuously” means withdrawing a reaction product while introducing a starting material into a reactor without interrupting the chemical reaction.
In this apparatus, the reaction fluid containing the catalyst reaches a surface of the filter by being stirred with a stirrer. Next, only the liquid phase of the reaction fluid passes through the filter and into the inside of the filter, whereby the catalyst particles are left on the filter surface. The liquid phase (containing a reaction product) which does not contain the catalyst is delivered to the outside of the reactor via a conduit which communicate with the filter. The catalyst on the filter surface are returned to the reaction fluid by being scratched from the filter surface by force exerted by the stirred fluid. The telomerization reaction can be carried out continuously by feeding the starting material into the reactor continuously while conducting the filtration and scratching.